The present invention relates generally to an energy control system for a hybrid electric vehicle and more particularly to a system and method for controlling an electric motor and engine during bleed and charge states of a parallel hybrid electric vehicle.
A hybrid electric vehicle has a propulsion system that consists of at least one electric motor that is utilized in some form with another power source. Most often the other power source is a gasoline or diesel engine.
Typically, the two power sources are configured in one of two ways, series and parallel. In a series hybrid the traction force to the vehicle""s wheels is provided strictly by the electric motor. Electric energy is stored in a battery and is used to power the motor whenever demanded by the driver. The other power source, i.e. an engine, is used to maintain the level of energy stored in the battery at a level that is adequate to supply power to the electric motor as needed. In a series hybrid the engine is not used to provide direct motive force to the wheels based on driver demand. All of the energy from the engine is stored in the battery, where it is used by the electric motor to propel the vehicle.
In a parallel hybrid, both the engine and the motor can be directly coupled to the vehicle""s wheels, so that both power sources can, independently, provide motive force for the vehicle. It should be noted that in a parallel hybrid, the engine is sometimes used to recharge the battery that supplies the motor, just as in a series hybrid.
In a specific configuration of a parallel hybrid, the motor only provides positive torque when it is used to boost the torque from the engine. This configuration requires far less energy from the battery and is often referred to as a Low Storage Requirement (LSR) architecture.
Bleed and Charge states of operation for a hybrid electric vehicle occur during periods when the battery""s state of charge (SOC) is regulated to a desired level. If the SOC is higher than a predetermined calibrated level, the electric motor is commanded to operate in a motoring state, which drains the battery of excess charge and returns it to an optimal SOC. This is known as the Bleed state. When the SOC is lower than a predetermined calibrated level, the electric motor is commanded to operate in a generating mode. The result is a recharging of the battery to optimal SOC levels, also known as the Charge state.
It is an object of the present invention to implement fundamental functions of a parallel hybrid electric vehicle. It is another object of the present invention to provide an energy control system for implementing the functions of a parallel hybrid electric vehicle.
It is a further object of the present invention to provide an algorithm for controlling the Bleed and Charge states of a hybrid electric vehicle. It is still a further object of the present invention to generate torque commands to the electric motor that drive the battery to operate at optimal state of charge (SOC) levels. It is yet a further object of the present invention to make the CHARGE/BLEED hybrid operating modes transparent to the driver.
In carrying out the above objects and other objects and features of the present invention, an algorithm is provided as part of a code for an overall Vehicle System Controller (VSC) that controls an electric motor and engine. The algorithm of the present invention generates torque commands to an electric motor that drives a battery to operate at optimal SOC levels. The particular implementation of the electric motor control in order to supply a commanded torque is application specific and will not be discussed herein. The algorithm of the present invention is part of the control code used to command torque values to the electric motor in order to operate the electric motor/internal combustion engine during Bleed and Charge states in a manner that is transparent to an operator of the electric vehicle.
According to the present invention, the algorithms for controlling Bleed and Charge states of an electric vehicle are essentially the same. The only difference lies in the sign of the commanded torque. The Bleed state has a positive torque, and the Charge state has a negative torque.
The algorithm of the present invention establishes the power level at which the battery is to be charged, or bled. Next, the algorithm calculates the torque to be commanded to the electric motor based on this power level. The present invention maintains a transparent transition during charging and/or bleeding by the way this torque command is defined as well as by compensating for the torque from the electric motor in an engine control unit (ECU). At certain motor speeds a calibrated limit is used to set the commanded torque in order to accomplish a transparent transition.
Other objects and advantages of the present invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.